1. Technical Field
The present invention relates to a technique for compressing a mat wrapped about a cylindrical catalyst.
2. Background Art
Engine exhaust gas contains carbon monoxide, hydrocarbons, nitrogen oxide, and other undesirable substances. In view of this fact, an exhaust gas cleaning device is currently mounted in the exhaust systems of vehicle engines and the like. An exhaust gas cleaning device acts to remove or detoxify undesirable substances. A method for manufacturing an exhaust gas cleaning device will be described with reference to the drawings.
A catalyst 201 having a circular cross-section is prepared, as shown in FIG. 11A hereof. A mat 202 is wrapped about the catalyst 201, as shown in FIG. 11B. At this point, the outside diameter of the mat 202 is D1.
The mat 202 is then compressed until the outside diameter reaches d1, as shown in FIG. 11C and is inserted in a metal pipe 203 shown in FIG. 11D. An exhaust gas cleaning device 200 is obtained thereby. The outside diameter d1 is determined with consideration given to the inside diameter of the pipe 203.
In FIG. 11D, the compressed mat 202 attempts to return to the state prior to compression. As a result, the mat 202 presses the inside surface of the pipe 203 and the outside surface of the catalyst 201. Frictional force is generated between the pipe 203 and the mat 202 and between the catalyst 201 and the mat 202 due to the pressing force. Concern that the catalyst 201 will be separated from the pipe 203 is eliminated due to the effect of the frictional force.
In the description above, the work of compressing the mat 202 wrapped about the catalyst 201 is important, and several types of apparatuses have been proposed to provide that effect. One such apparatus is described in Japanese Patent Application Laid-Open Publication No. 2005-315252 (JP 2005-315252 A). The structure of the mat compression apparatus is described below with reference to FIG. 12.
The mat compression apparatus 205 is composed of pressers 206 obtained by dividing a thick cylinder into eight partitions, and an external cylinder 207 that moveably supports the pressers 206 toward the mat 202, as shown in FIG. 12. The mat 202 is then compressed by simultaneously causing the eight pressers 206 to move toward a center point 208 of the catalyst 201.
The pressers 206, 206 move toward the center point 208 in the manner shown by arrows (1), (1), as shown in FIG. 13, which is an enlarged view of section 13 of FIG. 12. For this reason, a gap α1 between the presser 206 and an adjoining presser 206 is considerable at the position shown by an imaginary line, and a gap α2 is reduced at the position shown by a solid line. The gaps α1 and α2 are always provided because the movement of the pressers 206, 206 toward the center point 208 becomes impossible when the gap reaches zero.
The gap varies from α1 to α2 when such compression is carried out. A portion of the mat 202 at a position corresponding to the large gap α1 is drawn in by the pressers 206, 206. The portion of the mat 202 is sandwiched between the pressers 206, 206 and forms a convex section 209. The convex section 209 interferes with the cylindrical unit 203 in the process from FIGS. 11C to 11D.
In view of the above, a step for crushing and flattening the convex section 209 is required after the compression step. The labor involved in mat compression is increased when the steps for flattening become more numerous.
In view of the above, a mat compression technique is needed in which there is no concern that a convex section will be formed in the mat.